1. Field of the Invention
This invention relates to a stepless transmission using a V-belt, and more particularly to a V-belt type stepless transmission suitable for motor vehicles.
2. Description of the Prior Art
In conventional V-belt type stepless transmissions, change gear ratios (or reduction ratio) as well as increments or decrements in compressive belt gripping force of pulleys are usually controlled by hydraulic pressure. However, since this sort of hydraulic control is restricted by the cylinder volume of a hydraulic servo and the minimum oil pressure as required in other parts of a hydraulic circuit, it has been difficult to change the belt gripping force precisely according to variations in transmitted torque. Therefore, when using as a transmission of a motor vehicle or the like which involves large variations in torque, an unduly large contact pressure is often imposed on the friction surfaces of pulleys and V-belt, shortening their service life and lowering the efficiency of power transmission.